Last Updated 5:59 p.m. ET
The U.S. has launched cruise missiles against Libyan air defenses as part of the international military effort against Libyan leader Muammar Qaddafi.
CBS News national security correspondent David Martin confirms that the Pentagon launched 50-100 cruise missiles around 2 p.m. ET Saturday, following the French fighter jets' sorties over Benghazi.
The Pentagon said that 110-112 Tomahawk cruise missiles were fired from U.S. and U.K. warships and submarines, targeting "at least 20" key communication nodes and air defense systems in Libya.
Al Jazeera is reporting that the headquarters of the military academy near Misrata, used as a base for Qaddafdi's forces, has been hit, but that has not been confirmed.
President Barack Obama said it was not an outcome that the U.S. or its allies sought, but that Qaddafi has ignored the will of the international community to refrain from waging violence against his own people.
"The danger faced by the people of Libya has grown," Mr. Obama said in a statement from Brasilia in Brazil. "We cannot stand idly by when a tyrant tells his people that there will be no mercy and his forces step up their assaults on cities like Benghazi and Misrata where innocent men and women face brutality and death at the hands of their own government."
A senior military official has told CBS News that the U.S. will be on the "leading edge" of coalition efforts to enforce the U.N. resolution.
Operation Odyssey Dawn has two goals: prevent further attacks on civilians by Qaddafi's forces, and develop the ability to establish a no-fly zone by going after Qaddafi's integrated air defenses.
A French fighter jet fired Saturday on a Libyan military vehicle, the first reported offensive action against Qaddafi's forces, a French defense official said.
French Defense Ministry spokesman Thierry Burkhard said the strike happened at 1645 GMT Saturday.
Burkhard said the target was confirmed as a military vehicle, but it was not clear what kind. He said no hostile fire on the French jet has been reported.
It was the first reported offensive military action against Qaddafi's troops, since the U.N. Security Council approved a resolution on Thursday, authorizing operations to protect civilians in Libya.
France sent a dozen Mirage and Rafale jets Saturday to survey the one-time opposition stronghold of Benghazi and the 150 kilometer-by-100 kilometer no-fly zone, Burkhard said.
"All aircraft that enter into this zone could be shot down," he said.
At a press conference, Secretary-General of the Libyan Public Congress Mohammed al-Zawi called the air strikes a "barbaric aggression against the Libyan people," and claimed the attacks came after the Libyan government announced a ceasefire against "the armed militias which are part of Al Qaeda in the Islamic West."
Al-Zawi said civilians injured by the air strikes have filled hospitals.
Libyan television has also claimed that "civilian targets" have been killed, and that a hospital had been hit by missiles from what were referred to as "Crusaders," although there is no independent confirmation of casualties or damage. Libyan TV also claimed that a French fighter jet has been shot down, which the French military denied.
The strike came less than two hours after top officials from the United States, Europe and the Arab world agreed in Paris to launch a risky military operation to protect civilians from attacks by Qaddafi's forces.
It also came after Libyan government forces attacked Benghazi earlier Saturday, apparently ignoring a proclaimed cease-fire.
Libyan state TV said Libyans, including women and children, were having a sit-in at the Tripoli international airport, apparently to deter bombers. It showed footage of hundreds of mostly young men on the runway carrying green flags and signs in support of Qaddafi.
French President Nicolas Sarkozy said after an emergency summit in Paris that French jets were already targeting Qaddafi's forces. The 22 participants in Saturday's summit "agreed to put in place all the means necessary, in particular military" to make Qaddafi respect a U.N. Security Council resolution Thursday demanding a cease-fire, Sarkozy said.
Speaking in Brazil Saturday, President Barack Obama said that the U.S. and its allies are prepared to act with urgency to end violence against civilians in Libya.
"Our consensus was strong, and our resolve is clear. The people of Libya must be protected, and in the absence of an immediate end to the violence against civilians our coalition is prepared to act, and to act with urgency," Mr. Obama said on the first day of a three-country Latin American tour.
Speaking in Paris on Saturday, Secretary of State Hillary Clinton said the international community had every reason to think that Qaddafi would commit "unspeakable atrocities" if his actions were left unchecked.
Meanwhile, Russia's government said it regrets the start of an international military operation against Qaddafi's forces.
The Russian Foreign Ministry said in a statement that "Moscow notes with regret this armed action, taken in conjunction with the hastily approved U.N. Security Council resolution" allowing a no-fly zone over Libya.
Moscow urged "exhaustive measures to ensure the safety of foreign diplomatic missions and their staff."
American ships and aircraft stationed in and around the Mediterranean Sea did not participate in initial French air missions Saturday over Libya, but the U.S. prepared to launch a missile attack on Libyan air defenses, according to two U.S. officials familiar with the unfolding intervention.
One official said the U.S. intends to limit its involvement - at least in the initial stages - to helping protect French and other air missions by taking out Libyan air defenses.
An attack against those defenses with Navy sea-launched Tomahawk cruise missiles was planned for later Saturday, one official said. Both officials spoke on condition of anonymity because of the sensitivity of military operations.
The official said that depending on how Libyan forces responded to initial intervention by the French and others, the U.S. could launch additional attacks in support of allied forces. The intention was to leave it to other nations to patrol a no-fly zone over Libya once air defenses are silenced, the official said.
Qaddafi had tried to take advantage of the time lag between the U.N. resolution and the launch of the international operation, making a decisive strike on the Benghazi, Libya's second-largest city and the first major stronghold of the rebellion.
Crashing shells shook buildings, and the sounds of battle drew closer to the city center as its residents despaired. A doctor said 27 bodies were brought to the hospital by midday. By late in the day, warplanes could be heard overhead.
"Our planes are blocking the air attacks on the city" of Benghazi, he said, without elaborating. French planes have been readying for an attack in recent days.
In an open letter, Qaddafi warned: "You will regret it if you dare to intervene in our country."
Al Jazeera reported that Qaddafi's forces also resumed bombing the western cities of Misrata and Zintan.
Earlier Saturday, a plane was shot down over the outskirts of Benghazi, sending up a massive black cloud of smoke. An Associated Press reporter saw the plane go down in flames and heard the sound of artillery and crackling gunfire.
Before the plane went down, journalists heard what appeared to be airstrikes from it. Rebels cheered and celebrated at the crash, though the government denied a plane had gone down or that any towns were shelled on Saturday.
The fighting galvanized the people of Benghazi, with young men collecting bottles to make gasoline bombs. Some residents dragged bed frames and metal scraps into the streets to make roadblocks.
Abdel-Hafez, a 49-year-old Benghazi resident, said rebels and government soldiers were fighting on a university campus on the south side of the city, with government tanks moving in, followed by ground troops. In the city center, tank fire drew closer and rebel shouts rang out.
At a news conference in the capital, Tripoli, the government spokesman read letters from Qaddafi to President Barack Obama and others involved in the international effort.
"Libya is not yours. Libya is for the Libyans. The Security Council resolution is invalid," he said in the letter to Sarkozy, British Prime Minister David Cameron, and U.N. Secretary-General Ban Ki-Moon.
To Obama, the Libyan leader was slightly more conciliatory: "If you had found them taking over American cities with armed force, tell me what you would do."
Government spokesman Moussa Ibrahim said the rebels and not Qaddafi's forces broke a cease-fire called by the government.
"Our armed forces continue to retreat and hide, but the rebels keep shelling us and provoking us," Musa told The Associated Press.
In a joint statement to Qaddafi late Friday, the United States, Britain and France backed by unspecified Arab countries called on Qaddafi to end his troops' advance toward Benghazi and pull them out of the cities of Misrata, Ajdabiya and Zawiya. It also called for the restoration of water, electricity and gas services in all areas. It said Libyans must be able to receive humanitarian aid or the "international community will make him suffer the consequences" with military action.
In Benghazi, crowds gathered at the courthouse that is the de facto rebel headquarters. About 200 people were in the area, drinking tea and talking. Some brought a tank and a mounted anti-aircraft gun they said they had captured today.
Dr. Gebreil Hewadi of the Jalaa Hospital and a member of the rebel health committee said that 27 dead had been taken to the hospital since Friday night.
Misrata, Libya's third-largest city and the last held by rebels in the west, came under sustained assault well after the cease-fire announcement, according to rebels and a doctor there. The doctor, who spoke on condition of anonymity because he feared reprisals, said Qaddafi's snipers were on rooftops and his forces were searching homes for rebels.
Foreign Minister Moussa Koussa said that Libyan officials had informed the U.N. and the Security Council that the government was holding to the cease-fire and called for a team of foreign observers to verify that.
"The nation is respecting all the commitments put on it by the international community," he said, leaving the podium before answering any questions about Benghazi.
In the course of the rebellion, Libya has gone from a once-promising economy with the largest proven oil reserves in Africa to a country in turmoil. The foreign workers that underpinned the oil industry have fled; production and exports have all but ground to a halt; and its currency is down 30 percent in just two weeks.
The oil minister, Shukri Ghanem, held a news conference calling on foreign oil companies to send back their workers. He said the government would honor all its contracts.
"It is not our intention to violate any of these agreements and we hope that from their part they will honor this agreement and they will send back their workforces," he said.
Italy, which had been the main buyer for Libyan oil, offered the use of seven air and navy bases already housing U.S., NATO and Italian forces to enforce the no-fly zone over Libya.
Italy's defense minister, Ignazio La Russa, said Saturday that Italy wasn't just "renting out" its bases for others to use but was prepared to offer "moderate but determined" military support.